my catalytic converters are making this funny noise, i know that is illegal to take them out, ( in KY they dont inspect cars) and is expensive to replace them. Do you think it would be ok to cut them and break the inside stuff and put them back on?
i have done that on a lot of mitsubishi and honda cars, the check engine light didnt come on because i did not mess with the oxygen sensors. on japanese cars it also gives a bit of HP...i dont know what would do on a bmw, havent done that before.
can anybody help? :help
thanx

I don't think you should do that to a BMW :nono . If it were a MB then I say go for it :buttrock .

my catalytic converters are making this funny noise, i know that is illegal to take them out, ( in KY they dont inspect cars) and is expensive to replace them. Do you think it would be ok to cut them and break the inside stuff and put them back on?
i have done that on a lot of mitsubishi and honda cars, the check engine light didnt come on because i did not mess with the oxygen sensors. on japanese cars it also gives a bit of HP...i dont know what would do on a bmw, havent done that before.
can anybody help? :help
thanx

My BMW is the only car I have running cats :) My Dad gutted his factory cat and welded in a piece of straight pipe through the middle. As long as your engine is running properly, you'll pass emissions no problem.

But these BMW's are pickly little creatures. So I wouldn't be surprised if it started throwing up error codes because of it. But if I was in the position where I was buying new cat's anyways, I wouldn't hesitate to dismantle the factory units and weld in some straight pipe to see if I could get by without tripping any error codes.

do u think will harm my engine in the long run? i am not going to put a straight pipe, im just going to empty the them and weld them back on

do u think will harm my engine in the long run? i am not going to put a straight pipe, im just going to empty the them and weld them back on

Hell no. Cat's are a restriction to the engine and serve no purpose other than to clean emissions for the environment. But a clean running engine will pass smog requirements without a cat in Washington. They don't even run a mirror undre the car anymore to check for smog equipment. I gut the cats and re-install just in case they start checking again. Save myself some trouble. I'm sure other states such as California are much more strict however.

Also, I would weld in a straight pipe if I were you. I"m not sure of construction of the BMW cats, but on the ones I"ve done there is nothing to guide the exhaust through after the insides are removed. In essence you will create a turbulance chamber which could restrict the flow. You need a straight pipe through the middle to guide the gasses through. It's really easy to do. You can get a straight piece of pipe at almost any auto parts store.

nice nice :D :D i am going to do it tomorrow morning. i will let u know with pictures and details... thanks a lot guys!

how will you bypass the information the O2 sensors send back to the OBDII re: mixture? I haven't heard of anyone running a modern BMW without cats. Results seem to be that the engine just won't run correctly.

Any results BasSPoweR?

WOOOOOhhhhhhhhhooooooooooo!!! :alright
FINALLY! im done, it took me around 6 hours (no help, just me) to take them appart and fix them.

I took the car over my uncles place, he owns a garage, so i could use the lift.
it was a piece of cake! all u need is a 21mm wrench for the oxygen sensors, a 13mm socket for the clamping bushings.

You dont need to cut or weld anything whatsoever. once u take the EXHAUST PIPE down just take a long thin steel rod and put it in from the shotrer side of the pipe and start hitting it untill u clean the inside stuff.
it took me around 15 minutes each converter to clean it. then get a cloth hanger and pull out the 2 round flexible rings that they are inside the converters.
after u get done cleaning it get a vacum cleaner and vacum the inside dust.
Put them back and thats it!

it took me a bit longer because i broke 2 HEX BOLTs that hold the EXHAUST MANIFOLD with the exhaust pipe :mad wich i had to replace.( i found them at lowes for $0.80 each.)

There is no way u can tell that the catalyt converters are missing.
my check engine light did not came on.

i will post some pics tomorrow.

Also, I would weld in a straight pipe if I were you. I"m not sure of construction of the BMW cats, but on the ones I"ve done there is nothing to guide the exhaust through after the insides are removed. In essence you will create a turbulance chamber which could restrict the flow. You need a straight pipe through the middle to guide the gasses through.

I don't know how much it matters or how much turbulance it really creates. I have a TT Z06 pushing 750rwhp that I ran a no CAT test pipe (off road pipe) to test back pressure and it seems to do fine. The below dynograph is with HI FLOW catalytic converters...smog legal. I agree that gutting the cats forms an expansion chamber...but I don't know how much performance reduction is occurrying because of it.

https://www.aandacorvette.com/images/items/kevin%201.JPG


How loud is your car now that you gutted the cats?????

i drove it in town for a bit, i couldnt tell the difference on low RPM between 1000-3.400. but when i stept on the gas pedal and went up to 6.200 it sounded a bit different.
i even put it in a closed garage, and there i could tell that the sound is different and a little bit louder.

I had a friend telling me that i can reduce that loudness by puting a silencer where ur cats are with the same diameter as ur catalyt converters
i dont think this would work thogh...
what do u think?

i drove it in town for a bit, i couldnt tell the difference on low RPM between 1000-3.400. but when i stept on the gas pedal and went up to 6.200 it sounded a bit different.
i even put it in a closed garage, and there i could tell that the sound is different and a little bit louder.

I had a friend telling me that i can reduce that loudness by puting a silencer where ur cats are with the same diameter as ur catalyt converters
i dont think this would work thogh...
what do u think?


Short silencers are used frequently to reduce sound. It would work, and might even fool a few diagnostic people into thinking you still have cat's under there.

i still have the cats on, but its only the housing. The inside is empty..i still can fool any inspection. :D

i still have the cats on, but its only the housing. The inside is empty..i still can fool any inspection. :D
After driving a few hundred miles please tell us if your check engine light ever comes on. I am really interested in knowing what your ECU is doing now there is no cat, as well as how much it is altering the A/F mixture as a result.

what if it comes on? what does that mean?
utill now nothing came on, i sure it gave a bit HP... before i take them out when i use to accelerate it was vibrating for 2 seconds. Now is perfect. I will let you know if anything comes on or goes wrong.

my catalytic converters are making this funny noise, i know that is illegal to take them out, ( in KY they dont inspect cars) and is expensive to replace them. Do you think it would be ok to cut them and break the inside stuff and put them back on?
i have done that on a lot of mitsubishi and honda cars, the check engine light didnt come on because i did not mess with the oxygen sensors. on japanese cars it also gives a bit of HP...i dont know what would do on a bmw, havent done that before.
can anybody help? :help
thanx

I did that last year to buy me some time, bad idea:

- illegal
- got nasty fumes standing behind the car
- failed emissions
- pain in the ass to do

I ended up cutting them back out and welded in hi-flow aftermarket cats @ $100 a pop and passed emissions with flying colors...

too late, i already took them out. but if my check engine light ever lights up i might have to put new ones on. where did u get them for $100?

I did that last year to buy me some time, bad idea:

- illegal
- got nasty fumes standing behind the car
- failed emissions
- pain in the ass to do

I ended up cutting them back out and welded in hi-flow aftermarket cats @ $100 a pop and passed emissions with flying colors...

Warning: He has OBDI. 96' and later e38's are OBDII and dont like aftermarket cats. Throws error codes.

so..that means DONT put any other aftermarket cats on?

Aftermarket cats do not throw codes if they are installed correctly. I have a set of Magnaflow high performace cats that have been on the car for 5 months and 10,000 miles. No problems what so ever and a noticeable gain in acceleration. Total cost for installation and parts $464.28.

did u buy them online? or you found them over the mufler shop?

Got the cats from the same shop that did the install.

I did that last year to buy me some time, bad idea:

- illegal

So is speeding :D

- got nasty fumes standing behind the car

Just like all the old cars built up to the early 70's. I like that smell personally.

- failed emissions

Must have something to do with the computerized vehicles. My Dad's Silverado passes no problem without cats.

- pain in the ass to do

It has to be done anyways if your cat's are bad. The bad cat would hit the trash either way, so you might as well experiement IMO. If the vehicle still meets emission regulations I don't see any reason not to do it.

you can get them from Jegs or Summit or even a local speed shop...

Instead of gutting the cats, why not just replace with a straight pipe? Then you could replace the cats for emissions testing if necessary, or if there's ever a problem running without cats.

I've been considering this for a while.... my cats are toast. Bass -- everything good so far??

Instead of gutting the cats, why not just replace with a straight pipe? Then you could replace the cats for emissions testing if necessary, or if there's ever a problem running without cats.

I've been considering this for a while.... my cats are toast. Bass -- everything good so far??

Well, his cats were bad anyways. So I would just gut them and give it a shot before throwing them in the dumpster. Then you have the added benefit of appearing like you still have a legal emissions system. A straight pipe is a dead giveaway and will cause problems in states where they inspect.

There is no problem AT ALL!! i took it for a trip to indiana (2 hours from here) I believe is faster now, i didnt cut or weld anything. The car runs better now.
I asked my uncle, he is an A.Manager in Toyotas factory in prinston IN if it will harm my engine, and he told me that the engine runs better without them and it also gives it more horsepower.
He also told me that the cars that they are exporting to the arab countries (S.arabia,kuwait,....) their emissions are a lot more than the american cars, some of them he said they dont have cats on at all.
The cats are just a filter for the enviromet.